Screw-in pacing lead

Abstract

A lead for use with a pacemaker in a pacing system, the lead having at least one electrode placed at its distal tip and a helical fixation member at the lead distal tip for screwing the lead into a patient's heart wall. The helical member is composed of shape-memory metal and until use is encapsulated in a shrunken state with a diameter less than the diameter of the lead casing. The encapsulation material is preferably mannitol or a like material which dissolves when placed in the human heart. The shape-memory helix when released from the encapsulation material assumes an expanded diameter, greater than electrode diameter and preferably greater, so that when it is screwed into the heart wall, the helical coils are displaced radially away from the outer edge of the tip electrode. By this design, the damage to the heart tissue caused by the helix does not affect the heart wall immediately proximate to the tip electrode.

What is claimed is: 
     
       1. A lead for use with a pacemaker in a pacemaker system, having a proximal end for attachment to said pacemaker and a distal end having an electrode at the tip thereof, said electrode having a first diameter, a substantially cylindrical tube running the length of said lead between said proximal and distal ends, said tube having a second diameter greater than said first electrode diameter, conductor means within said tube length for conducting electrical signals between said proximal end and said tip electrode, and screwtype fixation means connected to said distal end for anchoring said distal end into a patient's heart, said fixation means further comprising a helix having memory metal, a coating encapsulating said helix and holding it in a state such that it has a third diameter less than said second body diameter, said coating comprising a material which dissolves when placed in file human heart, said helix expanding to a greater diameter than said tube second diameter when said coating dissolves and releases said helix. 
     
     
       2. The lead as described in claim 1, wherein said coating is temperature sensitive. 
     
     
       3. The lead as described in claim 1, wherein said coating comprises mannitol. 
     
     
       4. The lead as described in claim 1, wherein said helix and said electrode are aligned substantially concentrically with the axis of said cylindrical tube.